Electric generator having multiple electrical machines

ABSTRACT

An electric generator that converts mechanical energy to electrical energy includes, among other things, a first axial flow electrical machine that includes a first rotor mounted in rotation about a first axis and surrounding a first stator; a second axial flow electrical machine that includes a second rotor coaxial to the first rotor and surrounding a second stator; and first azimuthal securing means that joins together the first and second rotors so that the first and second rotors can be simultaneously set in rotation about the first axis. The electrical generator may be used as part of a wind turbine.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of U.S.application Ser. No. 15/787,190 filed on 18 Oct. 2017, (now allowed),which is a continuation of U.S. application Ser. No. 14/432,491 filed on31 Mar. 2015, (abandoned), which is a U.S. National Stage application ofInternational Application No. PCT/FR2013/052120 filed 17 Sep. 2013,which claims priority to French Application No. 1259253 filed 1 Oct.2012, the entire disclosures of which are hereby incorporated byreference in their entireties.

BACKGROUND OF THE INVENTION

The subject of the present invention is an electric generator allowingthe conversion of mechanical energy to electrical energy.

In its main application the electric generator is used for convertingthe mechanical energy of a wind turbine. However, the electric generatorcan also be used in numerous other sectors, such as electricity powerstations grouped with a steam turbine or gas turbine, or in hydraulicpower stations.

In the remainder of the application, the advantages are detailed of anelectric generator comprising at least one electrical machine, theelectrical machine being an axial flow alternator able to be integratedin a wind turbine.

On the basis of this example, persons skilled in the art will easilyinfer the adaptations required to produce the electric generator forother applications such as those aforementioned.

For several years, the dimensions of wind turbines and in particular thediameter of their blades have undergone considerable increase to obtainvery high electric power without multiplying the number of windturbines. Thereafter the electrical machines equipping these windturbines have become increasingly more voluminous.

These changes to the size of electrical machines require the adapting ofproduction tooling, complicate installation and maintenance, increasemanufacturing and installation costs and accentuate the visual impact ofsuch devices.

One solution is proposed in document FR 2 926 935 held by the applicant,which describes an electrical machine comprising a rotor surrounding astator, the rotor and stator both being formed of different sectionsjoined to one another. The structure of the rotor and of the statortherefore allows electrical machines to be produced of varying size,using one and the same production tooling, and being easier to installthan electrical machines of same size comprising a rotor and stator eachformed of a single piece.

However this solution does not solve all the problems previouslymentioned amongst which the visual impact of wind turbines of largesize.

SUBJECT AND SUMMARY OF THE INVENTION

It is the objective of the present invention to propose an electricgenerator allowing very high electrical power to be obtained without asignificant increase in the dimensions of the electric generator. Thisobjective is reached through the fact that the invention concerns anelectric generator allowing the conversion of mechanical energy toelectrical energy, the electric generator at least comprising:

a first axial flow electrical machine comprising a first rotor mountedin rotation about a first axis and surrounding a first stator togenerate a first magnetic flow;

a second axial flow electrical machine comprising a second rotorseparate from the first rotor, which is coaxial to the first rotor andsurrounds a second stator to generate a second magnetic flow;

first azimuthal securing means to join the first and second rotors sothat the first and second rotors can be simultaneously placed inrotation about the first axis for the simultaneous generation of thefirst and second magnetic flows.

This device therefore allows the accumulation of the electric powersgenerated by the first and second electrical machines, to obtain greaterelectrical energy than would be obtained by an electric generator onlycomprising one of the first and second electrical machines.

By azimuthal is meant the direction perpendicular both to the axialdirection of the first and second rotors, defined by the first axisabout which the first and second rotors are rotatably mounted, and tothe radial direction of the first and second rotors, defined by one ofthe radii of one of the first and second rotors. Azimuthal joining hasthe effect that the first and second rotors cannot rotate relative toone another about their axial directions. Said otherwise, azimuthaljoining of two rotors prevents relative azimuthal movement between thesetwo rotors. The rotation of one of the rotors therefore causes therotation of the other.

Since the first and second rotors are secured to one another, they areset in rotation simultaneously, for example but not limited thereto bythe hub of a wind turbine.

In addition, the complexity of the manufacture of the electric generatorof the present invention is similar to that of the manufacture of eachof the first and second electrical machines; its manufacturing cost isequal to or slightly higher than the manufacturing costs of the firstand second electrical machines.

Its installation and maintenance are significantly simplified comparedwith an electric generator generating similar electrical power andcomprising a single electrical machine, the dimensions of this singleelectrical machine being substantially larger than those of each of thefirst and second electrical machines forming the generator of thepresent invention.

In the event of faulty functioning of one or other of the electricalmachines, the electric generator of the present invention is able tocontinue generating electric energy, the electric generator therebyremaining available. This characteristic is particularly advantageouswhen the electric generator is used to equip a wind turbine installed inareas having difficult access, in open sea for example, the servicingtime to repair the faulty element then possibly being particularlylengthy.

The radial bulk of the electric generator of the present invention isthe same as that of an electrical machine of larger size.

By radial bulk of the generator is meant the span defined by the firstand second electrical machines in a plane perpendicular to the firstaxis.

Preferably, the first and second rotors respectively surround the firstand second stators circumferentially.

In other words, the first and second rotors extend along the respectivecircumference of the first and second stators, surrounding the same.

It will therefore be understood that the first and second rotors eachdefine an annular cavity or housing configured to receive the first andsecond stators respectively.

The annular housings thus defined by the first and second rotors arejoined together by the first azimuthal securing means.

Preferably, the first and second electrical machines are identical, sothat the complexity of the manufacture of the electric generator isthereby further reduced. The radial bulk of the electric generator isthen the radial bulk of an electric generator only comprising a singleelectrical machine.

Advantageously, the first and second electrical machines are able toimplement different technologies, to reduce the probability that theelectrical machines may simultaneously develop a fault.

The invention is described below in a series of variants of embodimentwhich can be considered alone or in combination with one or more of theothers.

Advantageously, the first and second rotors each comprise first andsecond walls, arranged either side of the first and second statorsrespectively, which define a first and second annular housingrespectively in which the first and second stators are housed, thesecond wall of the first rotor and the first wall of the second rotorbeing arranged facing one another and the first azimuthal securing meansbeing configured to join together the second wall of the first rotor andthe first wall of the second rotor in an azimuthal direction. Azimuthalcoupling is therefore obtained between the first and second rotors.

It will therefore be understood that in the electrical machines of theelectric generator of the present invention, each stator is arrangedbetween the first and second walls of the corresponding rotor, the firstand second walls of each of the rotors defining a circumferentialhousing. It will also be understood that the first and second electricalmachines are placed side by side, and that they are secured to oneanother by cooperation of their adjacent walls. It is thereforeunderstood that in a plane containing the first axis the electricgenerator has an axis of symmetry positioned between the second wall ofthe first machine and the first wall of the second machine.

With this arrangement, it is sufficient that one of the electricalmachines is driven in rotation about the first axis so that it willcause the other electrical machine also to be driven in rotation aboutthe first axis.

Additionally, with this arrangement, it will be understood that thestructure of the stators need not be modified so that they can bemounted on the electric generator of the present invention, therebyavoiding the generation of additional costs for the manufacture andassembly thereof. Also, it will be understood that the first securingmeans are mounted on the outer surface of the adjacent walls of thefirst and second rotors, so that the inner structure of the rotors andthe functioning of the electrical machines are not modified by thejoining of the first and second electrical machines.

By outer surface of the walls is meant the surface of the rotor wallsopposite the surface arranged facing the first and second stator withwhich the first and second rotors respectively cooperate.

Preferably the first and second walls of the first and second rotors areof annular shape.

Advantageously the first and second walls of the first and second rotorsare in the shape of coaxial discs.

Preferably the first and second stators are also coaxial discs.

Advantageously the first and second stators are coaxial to the first andsecond rotors.

Preferably, the first azimuthal securing means also form axial securingmeans configured to couple together the first and second rotors alongthe first axis. In other words, they prevent any axial movement betweenthe first and second rotors. The only degree of freedom is radialmovement which is only permitted during mounting and dismountingoperations of the electric generator of the present invention.

Advantageously, the first azimuthal securing means comprise a slidingconnection enabling radial movement of the second wall of the firstrotor relative to the first wall of the second rotor when assembling theelectric generator.

With this arrangement, it will be understood that the first and secondrotors are secured together via radial translation along an axisperpendicular to the first axis, so that the axial space required forassembling of the electric generator is equal to the axial space takenup the electric generator once it has been mounted.

By axial space is to be understood the portion of the first axis alongwhich the first and second electrical machines are arranged in theelectric generator of the present invention.

It will therefore be understood that the first azimuthal securing meansare moved radially relative to the first and second rotors in order toassemble the electric generator of the present invention. The use of asliding connection therefore ensures a maintained constant gap betweenthe first and second rotors

Preferably the sliding connection comprises an outer slide formed on oneof the walls from among the second wall of the first rotor and the firstwall of the second rotor, and an inner slide formed on the other of thewalls from among the second wall of the first rotor and the first wallof the second rotor, the inner and outer slides being configured so thatthe inner slide slides in the outer slide at the time of assembling theelectric generator.

It will therefore be understood that the second wall of the first rotorand the first wall of the second rotor comprise outer and inner slidesformed on their outer surface so that it is possible to secure the twowalls to one another. With this arrangement, the manufacturing of therotors is identical to that of a rotor intended to equip an electricgenerator only comprising a single electrical machine, the inner andouter slides simply having to be added and secured onto the outersurfaces of the rotors.

Advantageously, the slide connection has a dovetail-shaped profile.

By dovetail is meant a slide connection which comprises a tenon oftrapezoid shape engaging in a groove of same shape to ensure the slidingconnection.

The sliding of the slides one in the other also provides for simplifiedmounting of the electric generator of the present invention, once theinner slide is engaged in the outer slide, the user only having totranslate the slides in relation to each other.

Advantageously, one of the first and second rotors is composed of atleast two sections and of assembly means allowing the joining of the twosections to each other, the first azimuthal securing means beingarranged on at least one of the sections.

With this arrangement, it is possible to manufacture and transport thedifferent sections of the rotor separately, the assembling together ofthe sections possibly being performed at the mounting site of theelectric generator of the present invention.

Additionally, the use of sections to form the rotor also allowselectrical machines of varying sizes to be produced, and in particularof large size using one same production tooling.

Preferably the two rotors are composed of at least two sections.

Advantageously, the two rotors comprise the same number of sections.

Advantageously, each section of the first rotor can be secured byazimuthal securing means to one of the sections of the second rotor.

Preferably, the electric generator also comprises attachment means tosecure the first and second stators.

With this configuration, the gap between the stators is kept constant.

Advantageously, the electric generator also comprises a third axial flowelectrical machine comprising a third rotor coaxial to the first rotorand surrounding a third stator to generate a third magnetic flow, andsecond azimuthal securing means to secure the third rotor to one of thefirst and second rotors so that the first, second and third rotors canbe simultaneously set in rotation about the first axis to generate thefirst, second and third magnetic flows simultaneously.

The third rotor therefore defines a third annular housing configured toreceive the third stator, the third annular housing being connected toone of the first and second annular housings by the second azimuthalsecuring means.

It will be understood that all the advantages detailed previously for anelectric generator comprising a first and second electrical machineremain true for the case in which the electric generator comprises threeelectrical machines. It is within easy reach of persons skilled in theart, from the structure of the electric generators described in thisapplication, to infer the structure of an electric generator which maycomprise four, five or more electrical machines. It is therefore easilypossible to have an electric generator of the desired power byassociating a suitable number of electrical machines.

The invention also concerns a wind turbine comprising a tower and hubmounted in rotation relative to the tower about an axis of rotation, thehub being driven in rotation by a spinner, the wind turbine alsocomprising an electric generator according to the present invention, thefirst and second rotors being mounted in rotation about the axis ofrotation.

Advantageously, at least one of the first and second rotors comprisessecuring means configured to secure the said at least one of the firstand second rotors to the hub.

With this configuration it will be understood that the spinner, via thesecuring means, drives the first and rotors in rotation. Therefore theelectric power produced by the wind turbine of the present invention,obtained by combining the first and second electrical machines, issubstantially higher than the power that would be produced by a windturbine of same size of which the electric generator only comprises oneof the first and second electrical machines.

Preferably the wind turbine comprises a flange connecting the hub to atleast one of the electrical machines, perforations being made in theflange to allow ventilation of the electrical machines.

Advantageously, the wind turbine comprises a ventilation systemcomprising at least one ventilation module formed of a fan and motor.

Preferably, the ventilation system comprises at least as manyventilation modules as there are electrical machines.

With this configuration, it will be understood that each of theventilation modules is intended to ventilate separately one of theelectrical machines. The configuration of the ventilation systemtherefore allows some ventilation modules to be placed in operationselectively to ventilate at least one of the electrical machines.

Advantageously, each electrical machine comprises a power converterconfigured to transfer the electric power generated by the electricalmachines onto the electricity grid allowing the conveying of electricenergy to consumers.

Advantageously, the wind turbine of the present invention comprises aselection system configured to set in operation independently each ofthe power converters of the electric generator.

It will therefore be understood that it is possible to optimise theyield of the electric generator, for example when wind power is low, byonly setting in operation some power converters. The selection systemalso allows the production time of electric energy to be distributedover the different electric machines so as to manage the wear thereof.

More generally it will be understood that the electric generator of thepresent invention comprises numerous modular factors: several electricalmachines can be combined with one another within one same electricgenerator, the different electrical machines can be of same or differentsize and power or have same or different properties, or they can applysame or different technologies, the rotors can be composed of severalsections, the stators can also be composed of several separate partsintended to be assembled, the ventilation system comprises severalventilation modules, each electrical machine is associated with aseparate power converter, . . . .

It will therefore be understood that starting from elementary componentssuch as the rotor sections, stator elements, ventilation modules, powerconverters, . . . , it is possible to produce a wind turbine which meetsall types of power and size requirements. As detailed in the foregoingwhen describing the electric generator comprising first and secondelectrical machines, said modular structure has multiple advantagesregarding cost and complexity of manufacture, the transport ofcomponents of the wind turbine to the assembly site, the dimensions ofthe assembled wind turbine, the maintenance thereof, its capacity togenerate electric energy continuously, despite unfavourable outsideconditions or faulty elements, . . . .

In addition, the invention also concerns a method for mounting a windturbine according to the present invention, the wind turbine comprisinga first and second electrical machine, the method comprising a stepduring which the first electrical machine is mounted on the windturbine, followed by a step during which the second stator is mounted onthe wind turbine, followed by a step during which the second rotor ismounted around the second stator and is secured to the first rotor.

Advantageously, it is therefore possible to replace one of theconstituent elements of one of the first and second machines withoutdismounting the assembly formed by the first and second electricalmachines.

Advantageously, the first and second electrical machines can be mountedtogether in accordance with the method, before the assembly formed bythe first and second electrical machines is mounted on the wind turbine,for example to carry out testing thereof.

Finally, the invention concerns a method for assembling a wind turbineof the present invention, the wind turbine comprising a first, a secondand a third electrical machine, the method comprising a step duringwhich the first electrical machine is mounted on the wind turbine,followed by a step during which the second stator is mounted on the windturbine, followed by a step during which the third electrical machine ismounted on the wind turbine, followed by a step during which the secondrotor is mounted around the second stator and is secured to the firstand third rotors.

Advantageously the first, second and third electrical machines can bemounted together according to the method before the assembly formed bythe three electrical machines is mounted on the wind turbine.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will become moreclearly apparent and complete on reading the following description ofone preferred embodiment given as a non-limiting example and withreference to the appended drawings in which:

FIG. 1 schematically illustrates an example of an electric generatoraccording to the present invention, the electric generator comprising afirst and second electrical machine;

FIG. 2 schematically illustrates the first and second electricalmachines of the electric generator in FIG. 1, seen from overhead;

FIG. 3 schematically illustrates part of the first and second electricalmachines of the electric generator in FIG. 1;

FIG. 4 schematically illustrates part of the first and second electricalmachines of the electric generator in FIG. 1;

FIG. 5 schematically illustrates a step in the mounting of the electricgenerator in FIG. 1;

FIG. 6 schematically illustrates a wind turbine comprising the electricgenerator in FIG. 1; and

FIG. 7 schematically illustrates an example of an electric generatoraccording to the invention, the electric generator comprising a first, asecond and a third electrical machine.

DETAILED DESCRIPTION OF THE INVENTION

In the example illustrated in FIG. 1, the electric generator 10 of theinvention has a first axial flow electrical machine 100 formed by afirst rotor 102 mounted in rotation about a first axis X and surroundinga first stator 104. The electric generator 10 also has a second axialflow electrical machine 200 formed by a second rotor 202 also mounted inrotation about a first axis X and surrounding a second stator 204.

As illustrated in FIG. 1, the first rotor 102 has a U-shaped profile,but is not limited thereto; the first rotor 102 particularly comprisesfirst 106 and second 108 walls arranged either side of the first stator104. The first rotor 102 further comprises a first upper edge 110 whichconnects the first 106 and second 108 walls.

The first 106 and second 108 walls of the first rotor 102 each have anannular shape and define a first annular housing configured to receivethe first stator 104.

It will therefore be understood that the first rotor 102 surrounds thefirst stator 104 circumferentially. In other words, the first rotor 102extends along the circumference of the first stator 104 so as tosurround the latter.

Similarly the second rotor 202 has a U-shaped profile but is not limitedthereto; the second rotor 202 in particular comprises first 206 andsecond 208 walls arranged either side of the second stator 204 andconnected by a second upper edge 210.

Therefore, in similar manner to the first electrical machine 100, thefirst 206 and second 208 walls of the second rotor 202 are each ofannular shape, and define a second annular housing configured to receivethe second stator 204.

In other words, second rotor 202 surrounds the second stator 204circumferentially.

Without departing from the scope of the present invention, the first andsecond walls 106, 108, 206, 208 and the upper edges 110, 210 of each ofthe first and second rotors 102, 202 could form a single part having aprofile such that it surrounds the first 104 and second 204 statorsrespectively.

The electric generator 10 of the present invention also comprises firstsecuring means 12 arranged between the second wall 108 of the firstelectrical machine 100 and the first wall 206 of the second electricalmachine 200, which will be described in more detail in particular in thedescription of FIG. 2.

It will be understood that the first securing means 12 are configured tojoin the first and second circumferential housings defined by the first102 and second 202 rotors respectively.

The electric generator 10 also comprises first connecting means 14arranged between the first 100 and second 200 electrical machines. Asillustrated in FIG. 1, the upper end 15 of the first connecting means 14is arranged between the first 104 and second 204 stators and comprisesattaching means 16 configured to secure the first 104 and second 204stators.

The median portion of the first connecting means 14 comprises aperforation 18, and the lower portion thereof 20 comprises first 22 andsecond 24 attaching elements.

As illustrated in FIG. 1, the electric generator 10 also comprises first26 and second 28 bearings. The upper portion of the first bearing 26 issecured to the second wall 108 of the first rotor 102 of the firstelectrical machine 100 via first securing means 29; the lower portion ofthe first bearing 26 is secured to the upper end 15 of the firstconnecting means 14 via second securing means 30.

The upper portion of the second bearing 28 is secured to the lower end20 of the first connecting means 14 via second attaching elements 24;the lower portion of the second bearing 28 comprises coupling means 31.

As illustrated in the different Figures, the first and second 29, 30securing means, the first and second 22, 24 attaching elements and thecoupling means 31 can be formed of bolts; they may also be formed of anyother means allowing the securing together of several elements withoutdeparting from the scope of the invention.

Finally, the electric generator 10 comprises attaching means 33 mountedboth on the first wall 106 of the first rotor 102 of the firstelectrical machine 100 and on the second bearing 28 via coupling means31.

FIG. 2 gives a detailed illustration of the first azimuthal securingmeans 12.

In this Figure in which the first 102 and second 202 rotors areillustrated from above, it can be seen that the first azimuthal securingmeans 12 are formed of an outer slide 32 and inner slide 34.

The outer slide 32 is formed by first 36 and second 38 lateral portions,both formed on the first wall 206 of the second rotor 202. The spaceformed between the first 36 and second 38 lateral portions defines ahousing having a trapezoid-shaped profile.

The inner slide 34 is formed by a first 40 and second 42 side, bothformed on the second wall 108 of the first rotor 102 and which define asection of trapezoid shape configured to be contained in the housingdefined by the outer slide 32. The inner slide 34 could also be formedof a single part defining a section of trapezoid shape without departingfrom the scope of the invention. It will therefore be understood thatthe shape of the inner 34 and outer 32 slides is such that the innerslide 34 is able to slide in the outer slide 32 in longitudinaldirection L, the longitudinal direction L being defined by the lateralportions 36, 38 and the sides 40, 42 parallel to one another.

As can be seen in FIG. 2, the lateral portions 36, 38 and the sides 40,42 project from the first wall 206 of the second rotor 202 and thesecond wall 108 of the first rotor 102 respectively; for example but notlimited thereto the lateral portions 36, 38 and the sides 40, 42 aresecured by screwing or any other securing device onto the first wall 206of the second rotor 202 and onto the second wall 108 of the first rotor102.

It can therefore be seen that the first azimuthal securing means 12 havea dovetail-shaped profile.

It could also be contemplated, without departing from the scope of thepresent invention, that the first azimuthal securing means 12 could havea profile of different shape, or that the electric generator 10 couldhave an inner slide 34 and outer slide 32 respectively formed on thefirst wall 206 of the second rotor 202 and on the second wall 108 of thefirst rotor 102.

It will therefore be understood that the first azimuthal securing means12 comprise a slide connection in a longitudinal direction L, whichforms a radial direction of the first 102 and second 202 rotors, theslide connection being formed by the inner slide 34 and outer slide 32configured to slide in one another when mounting the electric generator10 of the present invention, so as to secure the first 102 and second202 rotors.

FIGS. 3 and 4 illustrate part of the first 100 and second 200 electricalmachine of the electric generator 10 of the present invention.

As illustrated in FIG. 3, the first rotor 102 is formed of severalsections 112, 112′ which comprise assembly orifices 114, 114′ formed onthe upper edges 110, 110′ for assembling of the sections 112, 112′, viaassembly means such as screws, but not limited thereto, passed throughthe assembly orifices 114, 114′. Any other assembly means could also beenvisaged without departing from the scope of the present invention.

The first and second walls 106, 108 of the first rotor 102 each definean inner surface and outer surface, the inner surfaces of the first andsecond walls 106, 108 being arranged facing one another and surroundingthe first stator 104. As illustrated in FIG. 3, magnetizing areas 116are arranged on the inner surfaces of the walls 106, 108, thesemagnetizing areas 116 forming the inductor portion of the magneticcircuit of the first electrical machine 100.

For example, but not limited thereto, the magnetizing areas 116 areformed by the superimposition of permanent magnets. It could also beenvisaged without departing from the scope of the present invention,that the inductor portion of the magnetic circuit of the firstelectrical machine 100 is formed of any other element such as coils forexample.

As illustrated in FIG. 3, the first 40 and second 42 sides of the innerslide 34 are formed on the outer surface of the second wall 108. Also,first matching means 118 are arranged on the outer surface of the secondwall 108.

The first stator 104 is formed by a first rim of which one portion 120is illustrated in FIG. 3; the portion 120 comprises radial notches 122in which first active modules are inserted 124.

The first active modules 124 form the induced part of the magneticcircuit of the first electrical machine 100.

It will therefore be understood from FIG. 3, that the first rim of thefirst stator 104 is advantageously formed of at least two portions 120,the portions 120 able to be easily assembled at the mounting site of theelectric generator 10 using conventional operations for those skilled inthe art such as welding or riveting for example.

It will also be understood that the shape of the sections 112, 112′ ofthe first rotor 102 makes it possible easily and precisely to positionthe inducing part in relation to the induced part of the first stator104.

Finally it will be understood that the assembling of the portions 120 ofthe first rim of the first stator 104 defines a disc the centre of whichhas an orifice for mounting of the first stator 104 in free rotation.The assembling of the sections 112, 112′ of the first rotor 102 definesa cylinder portion having an outer diameter of same or even slightlylarger size than the disc formed by the first stator 104, the cylinderportion formed by the first rotor 102 comprising two lateral edgesarranged perpendicular to the cylinder surface and configured to bearranged either side of the radial end of the disc formed by the firststator 104.

Similarly, and as illustrated in FIG. 4, the second rotor 202 is formedof several sections 212, 212′ comprising assembly orifices 214, 214′.The first and second walls 206, 208 each comprise an inner surface andan outer surface, magnetization areas 216 being arranged on the innersurfaces of the walls 206, 208.

As illustrated in FIG. 4, the first 36 and second 38 lateral portions ofthe outer slide 32 are formed on the outer surface of the first wall206. In addition, second matching means 218 are arranged on the outersurface of the first wall 206.

The second stator 204 is formed of a second rim, of which one portion220 is illustrated in FIG. 4; the portion 220 comprises second radialnotches 222 in which second active modules 224 are inserted.

It will be understood from FIGS. 3 and 4 that the sides 40, 42 and thelateral portions 36, 38 are respectively arranged symmetrically inrelation to a first R1 and second R2 radius of the first 102 and second202 rotors.

FIG. 5 illustrates a mounting step of the electric generator 10.

Initially the first connecting means 14 are mounted on the secondbearing 28, via cooperation between second attaching elements 24 and theupper part of the second bearing 28.

The portions 120 of the first rim of the first stator 104 are thenmounted on the upper end 15 of the first connecting means 14, and thefirst bearing 26 is also mounted, for example but not limited thereto bywelding or riveting, on the upper end 15 of the first connecting means14.

As detailed previously in connection with FIG. 3, the sections 112, 112′of the first rotor 102 are then mounted around the first stator 104, thesections 112, 112′ being secured via their assembly orifices 114, 114′and assembly means, and the radial engaging of the sections 112, 112′around the first stator 104 is limited by the presence of the firstbearing 26; in particular, the first securing means 29 allow thesecuring together of the second wall 108 of the first rotor 102 and thefirst bearing 26.

Next, the portions 220 of the second rim of the second stator 204 aremounted on the attaching means 16 of the upper end 15 of the connectingmeans 14. In particular, the attaching means 16 define a first andsecond longitudinal end, the first and second stators 104, 204 beingrespectively mounted on each of the longitudinal ends, the first bearing26 being mounted between the two longitudinal ends.

Thereafter and as illustrated in FIG. 5, the sections 212, 212′ of thesecond rotor 202 are moved radially relative to the sections 112, 112′of the first rotor 102.

For example, but not limited thereto, the first and second rotors 102,202 each comprise the same number of sections, each section 112, 112′,212, 212′ comprising first azimuthal securing means 12 and each section112, 112′ of the first rotor 102 being configured to cooperate with asection 212, 212′ of the second rotor 202.

It could also be contemplated, without departing from the scope of theinvention, that the first 102 and second 202 rotors do not comprise thesame number of sections or that the matching of the sections of thefirst and second rotors 102, 202 is only performed by some of theirsections.

It will therefore be understood, as illustrated in particular in FIG. 5,that the section 220 of the second rotor 202 is arranged above thesecond stator 204, the first and second walls 206, 208 being arranged oneach side of the second stator 204, and the first wall 206 of the secondrotor 202 is arranged facing the second wall 108 of the first rotor 102,the lower end 37 of the outer slide 32 formed on the second rotor 202being arranged opposite, even slightly above the upper end 39 of theinner slide 34 formed on the first rotor 102. The second rotor 202 canthen be moved radially relative to the first rotor 102, when mounting ordismounting the electric generator 10, so that the outer slide 32 slidesaround the inner slide 34. In this position in which the outer 32 andinner 34 slides cooperate, there is merging of the first R1 and secondR2 radii.

The second rotor 202 is therefore moved radially in relation to thefirst rotor 102 until the first 118 and second 218 matching means arearranged opposite one another to match the first 102 and second 202rotors. For example and not limited thereto, the matching means 118, 218can be formed by threaded holes and bolts, rivets or any other deviceallowing the matching of the first and second 102, 202 rotors. It couldalso be envisaged, without departing from the scope of the presentinvention, that there is an abutment on the first azimuthal securingmeans 12 allowing the limiting of radial movement of the second wall 108of the first rotor 102 relative to the first wall 206 of the secondrotor 202.

It will therefore be understood that the first azimuthal securing means12 have the effect that the first 102 and second 202 rotors are unableto rotate in relation to one another about the first axis X.

It will also be understood that the shape of the first azimuthalsecuring means 12, described in particular with reference to FIG. 2, issuch that the first azimuthal securing means 12 prevent any axialmovement relative to the first axis X between the first 102 and second202 rotors, thereby making it possible to maintain constant the distanceseparating the first 102 and second 202 rotors. It therefore appearsthat the first azimuthal securing means 12 also form axial securingmeans.

Without departing from the scope of the present invention, an electricgenerator 10 can also be envisaged of which the second rotor 202 issecured onto the first bearing 26, the second rotor 202 therefore notnecessarily comprising matching means to allow the second rotor 202 tobe matched directly with the first rotor 102.

FIG. 6 illustrates a wind turbine 50 comprising a hub 52 mounted inrotation about the first axis X, and a spinner 54 to drive the hub 52 inrotation about the first axis X; also, the first 100 and second 200electrical machines are mounted in the wind turbine 50. As illustratedin FIG. 6, the first and second stators 104, 204 and the first andsecond rotors 102, 202 are coaxial to one another, the first and second102, 202 rotors both being mounted in rotation about the first axis X.

The attaching means 33 mounted on the first wall 106 of the first rotor102 are also mounted on the hub 52. It will therefore be understood thatwhen the spinner 54 drives the hub 52 in rotation about the first axisX, it also drives the first rotor 102 in rotation about the first axisX, via the attaching means 33. Subsequently, since the first and secondrotors 102, 202 are secured by the first azimuthal securing means 12,the second rotor 202 is simultaneously driven in rotation about thefirst axis X.

For example but not limited thereto the attaching means 33 are formed ofa plate or metal sheet of which the lower and is attached to the hub 52and to the second bearing 28, for example by clamping the lower end ofthe metal sheet between the hub 52 and the second bearing 28.

As can be seen on examining FIG. 6, the wind turbine 50 is also formedof a frame 55 secured to a tower 57 on which the hub 52 is mounted inrotation. The first and second stators 104, 204 are mounted firstly onthe frame 55 of the wind turbine via first attaching elements 22 mountedon the lower end 20 of the first connecting means 14, and secondly onthe first and second bearings 26, 28; they are not driven in rotationabout the axis X. Therefore via respective cooperation between theinduced part of the first and second stators 104, 204 stators and theinducing part of the first and second rotors 102, 202, the first andsecond electrical machines 100, 200 respectively generate first andsecond magnetic flows.

As illustrated in FIG. 6, the wind turbine 50 also comprises aventilation system 56 which comprises at least one ventilation module 58formed of a fan and motor. The ventilation system 56 also comprises anaeration duct 60 directed towards the perforation 18 formed in themedian portion of the first connecting means 14.

Therefore and as shown by the arrows illustrating the cycle in FIG. 6,the ventilation system 56 allows the diffusing of a fluid e.g. air oftemperature T1 in the first and second electrical machines 100, 200. Theoperation of the first and second electrical machines 100, 200 and inparticular the rotation of the first 102 and second 202 rotors, tends toraise the temperature of the fluid which is then directed at temperatureT2, towards the ventilation system 56. Through heat exchange with theenvironment outside the wind turbine 50, the temperature of the fluid islowered to temperature T1, before the fluid is again directed into theaeration duct 60 towards the first and second electrical machines 100,200.

As detailed in particular with reference to FIGS. 3 and 4, the first 100and second 200 electrical machines have a modular structure and inparticular comprise several sections 112, 112′, 212, 212′ forming thefirst 102 and second 202 rotors, and several portions 120, 220 formingthe rims of the first 104 and second 204 stators. The first connectingmeans 14 subsequently define a circular shape coaxial with the stators104, 204 and may also, but not limited thereto, be formed of a pluralityof elements arranged between the first 100 and second 200 electricalmachines. It will also be understood that the perforations 18 formed inthe median part of the first connecting means 14 are not necessarilydistributed homogeneously over the entire circular shape defined by thefirst connecting means 14. For example and not limited thereto, at somepositions of the circular shape defined by the first connecting means14, the median portion may not be perforated. Therefore the ventilationsystem 56 allows the ventilation of the first 100 and second 200electrical machines, the perforations 18 formed in the first connectingmeans 14 directing the fluid towards the first machine 100, whereas thepositions of the circular shape defined by the first connecting means 14in which no perforation is formed direct the fluid towards the secondelectrical machine 200.

In addition, the ventilation system 56 may be formed of severalventilation modules 58. For example and not limited thereto, to allowhomogenous ventilation of the electrical machines 100, 200, the samenumber of ventilation modules 58 may be intended for the ventilation ofthe first 100 and second 200 electrical machines.

It will therefore be understood that the first connecting means 14indirectly connect the hub 52 to the first and second electricalmachines, 100, 200 and form a flange in which perforations 18 are madeto allow ventilation of the electrical machines 100, 200.

As detailed in the foregoing, the first and second rotors 102, 202 andthe first and second stators 104, 204 are respectively formed ofpermanent magnets arranged around active modules. It will also beunderstood that the structure of the first and second electricalmachines 100, 200 of the present invention is identical. Nevertheless,it could just as well be envisaged without departing from the scope ofthe invention that in the electric generator 10 either one of the firstand second electrical machines 100, 200, or both, has induced andinducing parts of different structure; for example and not limitedthereto one of the electrical machines 100, 200 could comprise a coiledrotor.

FIG. 7 illustrates another embodiment of the electric generator 10according to the present invention which, in addition to the first andsecond electrical machines 100, 200, comprises a third electricalmachine 300 formed by a third rotor 302 coaxial to the first rotor 102and surrounding a third stator 304. In addition, the electric generator10 also comprises a third bearing 62 and second connecting means 66.

Similar to the first 100 and second 200 electrical machines previouslydescribed, the third rotor 302 of the third electrical machine 300comprises first 306 and second 308 walls both of annular shape, whichdefine a third annular housing configured to receive the third stator304. The third stator 304 is therefore surrounded by the third rotor 302circumferentially.

As illustrated in FIG. 7, the first 100 and third 300 electricalmachines are arranged symmetrically either side of the second electricalmachine 200.

It will be understood that to mount the electric generator 10 such asillustrated in FIG. 7, in similar manner to the mounting previouslydescribed, the first electrical machine 100 and the second stator 204are mounted on the first connecting means 14. The second connectingmeans 66 are then mounted on the second stator 204, the lower end of thesecond connecting means 66 being attached to the frame 55. The thirdelectrical machine 300 is then mounted on the second connecting means66, the first wall 306 of the third rotor 302 being mounted on the thirdbearing 62, whilst the third stator 304 is mounted on the upper end ofthe second connecting means 66.

The second rotor 202 is then engaged between the first 100 and third 300electrical machine, second azimuthal securing means 68 being formed onthe second wall 208 of the second electrical machine 200 and on thefirst wall 306 of the third electrical machine 300.

It will therefore be understood that the second azimuthal securing means68 are configured to join together the second and third annular housingsdefined by the second 202 and third 302 rotors respectively.

Therefore, and in similar manner to the foregoing description withreference in particular to FIG. 6, the spinner 54 drives the hub 52 inrotation about a first axis X, so that the first rotor 102 rotor isdriven in rotation about the first axis X via attaching means 33.Subsequently, the second 202 and third 302 rotors being secured to thefirst rotor 102 by the first 12 and second 68 azimuthal securing means,they are simultaneously driven in rotation about the first axis X. Sincethe first 104, second 204 and third 304 stators are not driven inrotation about the first axis X, through respective cooperation betweenthe induced part of the first, second and third stators 104, 204, 304and the inducing part of the first, second and third rotors 102, 202,302, the first, second and third electrical machines 100, 200, 300machines respectively generate a first, second and third magnetic flow.

The foregoing detailed characteristics regarding the structure of thefirst and second electrical machines 100, 200 evidently apply to thethird electrical machine 300. In particular, perforations can be made inthe second connecting means 66 to enable the ventilation system 56 toventilate the first, second and third electrical machines 100, 200, 300.

The entire foregoing description is given as an example and thereforedoes not limit the invention.

In particular, although the invention is particularly detailed forelectric generators comprising two or three electrical machines, it canbe extended directly and obviously to a higher number of electricalmachines.

What is claimed is:
 1. An electric generator allowing the conversion ofmechanical energy to electrical energy, comprising at least: a firstaxial flow electrical machine comprising a first rotor mounted inrotation about a first axis and surrounding a first stator to generate afirst magnetic flow; a second axial flow electrical machine comprising asecond rotor separate from the first rotor, which is coaxial to thefirst rotor and surrounds a second stator to generate a second magneticflow; and first azimuthal securing means to secure the first and secondrotors so that the first and second rotors can be simultaneously set inrotation about the first axis to generate the first and second magneticflows simultaneously.
 2. The electric generator according to claim 1,wherein the first azimuthal securing means also form axial securingmeans to secure together the first and second rotors along the firstaxis.
 3. The electric generator according to claim 1, wherein the firstand second rotors each comprise first and second walls arranged oneither side of the first and second stators respectively, so as torespectively define a first annular housing and a second annular housingconfigured to receive the first and second stators respectively, thesecond wall of the first rotor and the first wall of the second rotorbeing arranged facing one another and the first azimuthal securing meansbeing configured to join together the second wall of the first rotor andthe first wall of the second rotor in an azimuthal direction.
 4. Theelectric generator according to claim 3, wherein the first azimuthalsecuring means comprise a slide connection configured to allow radialmovement of the second wall of the first rotor relative to the firstwall of the second rotor when assembling the electric generator.
 5. Theelectric generator according to claim 4, wherein the slide connectioncomprises an outer slide formed on one of the walls from among thesecond wall of the first rotor and the first wall of the second rotor,and an inner slide formed on the other of the walls from among thesecond wall of the first rotor and the first wall of the second rotor,the inner and outer slides being configured so that the inner slideslides in the outer slide when assembling the electric generator.
 6. Theelectric generator according to claim 5, wherein the slide connectionhas a dovetail-shaped profile.
 7. The electric generator according toclaim 1, wherein one of the first and second rotors is composed of atleast two sections and of assembly means allowing the assemblingtogether of the two sections, the first azimuthal securing means beingarranged on at least one of the sections.
 8. The electric generatoraccording to claim 1, further comprising: attaching means to secure thefirst and second stators.
 9. The electric generator according to claim1, further comprising: a third axial flow electrical machine comprisinga third rotor coaxial to the first rotor and surrounding a third statorto generate a third magnetic flow, the electric generator furthercomprising second azimuthal securing means to secure the third rotor toone of the first and second rotors so that the first, second and thirdrotors can be simultaneously set in rotation about the first axis togenerate the first, second and third magnetic flows simultaneously. 10.A wind turbine comprising a tower and a hub mounted in rotation relativeto the tower about an axis of rotation, the hub being driven in rotationby a spinner, wherein the wind turbine also comprises an electricgenerator according to claim 1, the first and second rotors beingmounted in rotation about the axis of rotation.
 11. The wind turbineaccording to claim 10, wherein at least one of the first and secondrotors comprises attaching means configured to attach at least one ofthe first and second rotors to the hub.
 12. The wind turbine accordingto claim 10, further comprising: a flange connecting the hub to at leastone of the electrical machines, perforations being made in the flange toallow the ventilation of the at least one of the electrical machines.